Jazz neck won't bow either way, even with the trussrod nut removed

I can't get a 70's Jazz neck to bow either direction, even with the bullet truss rod nut removed and the neck off the bass.
I've been going crazy trying to lower the action, and I finally realized that I can barely even backbow it by hand.

Could the rod be frozen or locked in some way? I can tighten and loosen the nut at will. Could it be the top of the trussrod is locked somehow? It seems that if it freed up, the neck should bow both directions. It's solid, and won't bow either way. I was getting ready to try the backbow clamp trick, but no point if I can't even budge it backwards by (gently) holding the ends and pushing the middle with my knee.

Off the bass, nut removed, the neck is almost dead straight. Put it on the bass, and the strings bow it forward a little, but not crazy like it should with no nut on it. Could the metal ring right at the top of the rod be stuck to the rod freezing it in place? What would be the best way to un-stick that, if that's the issue?
This seems to be an odd one.

If the nut is using threads as you tighten then it should work til you hit the end of the threads. The weld may be broken at the anchor end allowing the rod itself to turn. Not good. On that type there is usually a plug on the heel where the anchor sits. One guy here drilled the plug out to access it. If your is like that you could drill it out and get it spot welded. You have to determine if the rod itself is turning.

Do those jazz necks have reinforcing rods?

Anyway you say under tension you have relief. Is it that much bow that you hate it? Are you just set on getting the neck flat?

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If the relief is ok as it is, and the action is too high (saddles can't go any lower),
then you need to add a strip of shim material at the inner end of the neck pocket
to tilt the neck backward. One or two slices of business card thick material.

Can you describe the behaviour of the truss rod and nut better? Does the nut
become tight abruptly? Does the resistance increase gradually?

Truss rods have less effect on a heavy neck, but heavy necks don't need the
effects of a truss rod as much as lighter necks, either.

I don't think the truss rod itself is turning at all. That seems fine. The threads on the rod are fine, and I even tried a brand new Fender bullet truss rod nut. It threads on immediately. It eventually gets snug and tight to a point where I'm not going to force it. If I can't bend the neck either way by hand without a trussrod nut, I don't see how tightening a nut would do anything but risk snapping something. I think it's just locked with the top trussrod ring at the headstock. That brings up a good question: Should there be a metal right there, or bare wood? I would assume the metal ring is stock, just like the metal bar in a Ric dual trussrod setup.

The neck is in great shape, as is the original truss rod nut. I don't think anyone abused it at all. I've even tried the spacer trick, but that doesn't help. The neck is dead straight right now, hanging on my wall with no truss rod nut on it. I would assume it should be curved with no nut.

If I string it up as-is, the action is just a little high. The string tension puts a slight curve in it, for about the first 5 frets, but I would think with no truss rod nut, it should be a huge curve from the middle of the neck. Enough to almost shoot an arrow. Maybe I'm wrong with that assumption.

The neck is on the thicker side, but not as much as a P bass. It just feels so solid like it won't budge either way. I carefully placed 2 small drops of WD-40 on the rod threads at the metal ring and I'll let it sit overnight with no trussrod nut. Maybe I'll have a nice curved neck by morning, but I'm not counting on it.

Now I want to look at the other way. If someone wanted to cause this, how would it be accomplished? Would someone coat the trussrod threads and metal ring with crazy glue to lock the rod in place so no adjustments could be made? Maybe if I could figure out how to cause the neck issue, then I could figure out how to resolve it if something was done to it.

I think you are saying the opposite of what I am about to link to?
After reading your post again this may not help, but it may give you some ideas. Whatever you do take your time. I loosened a rod on a garage sale bass, gave up on it about a week later it was ok. Took a whole week to move. Here is the link.http://chrisporro.com/?p=968

Under string tension, a good neck with a proper functioning truss rod should be able to be adjusted to a straight neck (no bow/relief) if this is not possible, I would first suspect that you are running out of threads and you need to put a washer under the nut.
Rocky

I am still not sure what you are seeing and expecting. It is not going to bend like an
arrow bow.

With the strings at tension, press down the E string at the 1st fret and the last fret.
There should be just a tiny gap between the string and the 8th fret. About .010' to .012".
That's about the thickness of a business card. If the truss rod adjustment can get you there,
it is doing all that it needs to.

I think everyone is missing the poster's issue. He is saying that the rod itself is seized somehow in relation to the wood it is anchored against, meaning that no adjusment can be possible in either direction.

To the OP- I don't know if the metal ring would be stock on a Fender of that era. It could well have been a washer that someone added to get a little more play out of the relief adjustment. As you said, if you can't bend the neck by hand to the point that the rod is obviously moving, then it must be stuck on something. Without any movement its hard to say if it is rusted to the washer or the threads are just stuck in the wood cavity, but if it was stuck to the washer alone I would expect that you'd still see movement of the rod when bending the neck back by hand (it would just prevent the nut from turning any farther and allowing adjustment) Does the washer seem like it has pushed/anchored itself into the wood? It seems likely that it has gotten itself stuck to the rod at least. I would recommend carefully dripping some lubricant down the truss rod and letting it settle in for a bit then try carefully pulling the neck back again to see if you got any play.

Here's my way to diagnose a wonky neck. Put a towel where your wall and floor meet. Rest the body of the bass there up against the wall and hold the neck firmly around where 1-3 frets are. Now, gently press your knee against the area where the neck bolts are towards the wall. Do this with the strings still on and tuned with the truss rod nut off. You should barely be able to make the strings touch the frets. If you can make them touch the frets, your neck is fine. You may have to tighten the nut 1/4 to 1/2 a turn, let your bass sit for a day and repeat until your action/relief is low enough to your taste. Also, note that necks aren't always bowed when the nut is removed and mine is always straight when loose as well. And I also had your same problem and took a week or two to get it low enough using the above 1/4 - 1/2 a turn a day method.

If you can't possibly touch the strings to the frets using my diagnosis method above, your neck may have a truss rod that is seized somehow into the slot near the nut. Test this theory with another person. Use the diagnosis method above and have someone else watch the truss rod to see if it moves in or out of the slot while you push the bass towards the wall a few times. If it does move and you still can't touch the strings to the frets, I have no idea lol.

Thank you again for all the replies.
Sunbeast said it best: "seized" trussrod. This has nothing to do with the nut, the rod threads, or anything like that. It's like as if a car's driveshaft was bolted to the road. The car couldn't be pushed forward or backwards.
The neck off the bass, trussrod nut removed, and the neck is dead straight. I can't bow it either way. I even checked it with a straight edge on the frets. Since I can't manually bend the neck, the rod won't move freely through the washer. It's like trying to bend a baseball bat. I'm certainly not going to force anything on the neck, especially with a trussrod nut. I think it's just simply frozen in place and maybe some WD-40 or something will unlock it.
I gave it a quick shot of WD-40 this morning, and the neck is hanging on the wall, with no trussrod nut installed. Hopefully when I'm done rotting in my cubicle for the day, I'll go home and find a slightly curved neck. If not, maybe I'll let the strings do the work of unfreezing the rod. I can put the neck back on the bass, without the trussrod nut, tune up the strings, give the rod 1 more shot of WD-40, and see if the strings can help unfreeze the rod. The rod doesn't appear stuck to the washer.
I added the picture below. I would guess that's the original metal ring (washer, spacer, whatever it's called).

just reading the text here, and looking at the pic ... a couple thoughts ... once wood takes a set for a period of time, it may not move at all, so expecting it to 'bow' onece the truss rod is backed off may be asking a bit much ...

... I would want to see if the truss rod itself is turning, and the way to do that is to use something that leaves the rod visible, as the 70's 'bullet' nut may not do it ...use a regular nut and figure out how to turn that and you will be able to see if the truss rod itself is turning (put a mark on it to help see this maybe) ... if if doesnt move, you may want to try to 'loosen' it (counterclockwise) and see what happens ... about the only way you can do this, is to put on two nuts ... screw one on just far enough to get the second on and then 'lock' them tight to each other .. you may want to find thinner nuts than regular, or turn them down so they are 'thinner' to both fit on the rod if that is an issue ... now if you can get a socket on them, you will be able to see if the truss rod itself turns to loosen (left)... if not, you have a seized rod ... if it turns left and not right, it may be maxed out and will not tighten any further ... then maybe the additional washers come into play ...

..a 'clamp' set up can be used to induce a bit of a natural backbow into the neck, so that after tension is applied it flattens out for you, so you end up with a straighter neck, and lower action ... this can take some time, and I have never tried in on a B and B neck, so just be careful with it ... if you search 'straightening a bowed neck' you should see pictures of the type of jig used for the 'clamp' type device I spoke of ...

Edit to add: ...probably a bit simple of a reply, but what are you using for strings on the bass? .. is it possible that you could just go to a lower (lighter gauge) tension string on the bass to minimize the relief under tension, and lower your action??

I'm not sure why you would expect a neck with the truss rod nut removed to be curved? I would expect it to be straight. I would expect a bass with a frozen truss rod to have a back bow with the strings off, assuming that the rod had some tension on it when it froze.

just be very careful and aware with the binding and blocks ... I have been fairly agressive with my clamping/blocking in the past, and I am not sure how the binding is going to respond to that flexion ... good luck!

it could be just a shadow or the angle that the picture was taken but.... it almost looks like the threads end beyond/past the washer. for the rod to work properly shouldn't the threads end behind the washer?

I've personally never owned a neck that I couldn't manually bend enough to see some movement of the truss rod coming out of the cavity, but that doesn't mean it isn't possible. Looking back at your original post I realize you never really mention what happens when you tighten the truss rod nut with the neck on the bass? Is the problem that it naturally has too little relief for your taste? Have you tried tightening the truss nut farther when on the bass to see if it has any effect even if it is already beyond your personal taste?

I have had a couple basses in the past that have held the tension of a light set of strings pretty well without the need for any help from the truss rod (so the nut could be basically loose and I'd still have a playable relief)- fortunately none of them had a relief that was too little for my taste or I would have a problem. I know some of the 70s Fenders were known for baseball bat-like necks, so it wouldn't be unbelievable that it was just super sturdy on its own merit. Though it is definitely possible that the rod is indeed seized as well especially given the age. At least it doesn't have a permanent back-bow!

Thank you all for the replies.
Nothing major at all. Simple 1 washer spacer over the trussrod, tightened snug when the strings are either loose or off, and a proper saddle lowering did the trick.
Pressing the first fret and last fret leaves a nice low "business card thickness" space under the 12th fret.
Patience, research, a small spacer, and a proper setup did the trick.
Thanks again.